Electric heater



Nov. 24, 1942. a 5. SMITH 2,302,808

ELECTRIC HEATER Filed July 31, 1941 2 Sheets-Sheet l 1942- E. 5. SMITH2,362,808

ELECTRIC HEATER Filed July 31, 1941 2 smu -521%: 2

Patented Nov. 24, 1942 ELECTRIC HEATER Elmore Stanley Smith, Weston,Ontario, Canada, assignor to Moflats, Limited, a corporation ApplicationJuly 31, 1941, Serial No. 404,943

6 Claim.

This is a continuation-impart of my patent application Serial No.209,438, filed in the United States Patent Omce on May 23, 1938,patented February 3, 1942, No. 2,272,136.

This invention relates to electric heaters and particularly to those ofthe sheathed element type having a casing or sheath formed of sheetmetal for enveloping a resistor and my object is to provide a heater ofthis type which is simple, strong, durable and easily made and whichwill form a good heat conducting path between the resistor and a cookingvessel placed on the heater whereby quick heating effects are obtained.

A further object is to so construct the sheath that it may beconveniently formed into a grid, the parts or convolutions of which arereadily anchored to suitable supporting means to hold said parts insuitable spaced relationship and with their upper surfaces insubstantially the same plane.

I attain my object by means of constructions which may be brieflydescribed as follows. The sheath is formed from a flat bottomed channelshaped strip of sheet metal, the channel having its margins directedlaterally from the sides thereof. After the channel has been filled withinsulating material and a resistor, a flat strip of metal is preferablyinserted and the upper parts of the sides of the channel are turnedinwardly to close the initially opened top of the channel. The saidmargins are thus brought into close relationship and project outwardlyfrom the sheath so that they may be conveniently welded or otherwisesecured together to seal the sheath and form a continuous rib or flange.The element may be bent to form a grid having the flat underside of thesheath uppermost and the flange depending from the sheath. The grid isanchored by any suitable means connecting together diflerent portions ofthe flange to hold parts of the grid in spaced relationship to oneanother and to prevent the grid from twisting. Preferably, parts of theflange are passed through openings in a channel member beneath the grid,and the lower ends of the said flange parts are deformed to secure themto the channel member.

The constructions are hereinafter more fully described and areillustrated in the accompanying drawings, in which Fig. 1 is aperspective view of a. strip of sheet metal, partly broken away. fromwhich the sheath is formed:

Fig. 2 a cross section of the sheath strip material formed into achannel having its margins laterally directed;

Fig. 3 a view similar to Fig. 2 showing insulating powder inserted inthe bottom of the channel:

Fig. 4 a view similar to Figures 2 and 3 showing the resistor inserted;

Fig. 5 a view similar to Figures 2, 3 and 4 showing more insulation anda narrow strip of metal inserted in the channel;

Fig. 6 a cross-sectional view showing diagram matically how the upperparts of the sides are bent in over the edges of the narrow strip whilethe latter is held in position;

Fig.- '7 a cross-sectional view showing the sheath completely closed;

Fig. 8 a plan view of a heater employing two of the sheathed elements;

Fig. 9 a cross-section on the lines 8!! in Figure 8;

Fig. 10 a cross-section on the lines Ill-III in Fig. 8;

Fig. 11 a front elevation of the heater;

Fig. 12 a perspective detail of the channel member to which the heateranchoring convolutions are secured;

Fig. 13 a bottom plan view showing more clearly the deformation of therib for attaching the element to the support;

Fig. 14 a view taken as indicated by the line ll of Fig. 13;

Fig. 15 a view similar to Fig. 13 showing a modified form; and

Fig. 16 a view taken as indicated by the line ll of Fig. 15

In the drawings like numerals of reference indicate corresponding partsin the different figures.

Referring to Figures 1 to 7, the heating element comprises a sheathformed of a strip of sheet metal which is first formed into a channel ihaving its margins 2 directed laterally from the sides 3. Insulatingpowder I having good heat conducting properties is deposited in the flatbottom I of the char-nel and pressure is applied to compact it thereinand shape it to receive a resistor 5. The latter may be a helical coilof resistance wire flattened out by passing it between rollers.

Each end of the resistor I is provided with a terminal or lead-in Iwhich may be welded or otherwise secured to the end of the wire 5. The

terminals 6 extend beyond the ends of the channel and are insulatedtherefrom by any suitable means such as a plurality of layers of mica.or a block I of other insulating material. The layers or blocks areadapted to be tightly received in the ends of the channel, to preventthe escape of powder therethrough, and preferably extend slightly beyondthe ends of the channel. More insulating powder 4 is then deposited inthe channel to cover the resistor and this powder is compressed tocompact the powder around the resistor. A strip of metal 8 is placed ontop of the insulating material 4" which is below the upper parts 3 ofthe sides of the channel. The said upper parts 3* are then bent in byany suitable means while a tongue 9 holds the strip 8 in place toprevent the insulating material from escaping. when the bent-in parts 3'engage the edges or the strip 8. the tongue i, which extends the fulllength of the strip, is withdrawn. The upper parts 3 are then again-forced-inwardly by any suitable means to their flnal position in whichthey overlie the strip 8. The channel is thus closed throughout itslength and the terminal insulations G- are also covered. Referring toFig. 7, it will be noted that the margins 2 new project outwardly fromthe body of the channel in close relationship to one another. The nextstep is to electrically weld these margins to seal the channel and thismay be accomplished by a series of closely spaced spot welds or by acontinuous weld produced by passing the margins 2 between two rollers ina resistance welding machine. The margins 2 when welded together form arib or flange 2" which extends the full length of the channel forpurposes which will be described later.

Preferably the insulating powder is slightly moist when it is insertedin the channel in which case the channel is placed in a drying oven toremove all traces of moisture from the compressed powder and theinterior of the channel before the latter is sealed. In practice, thepowder is compressed under a pressure of from 2 to 12 tons per squareinch. As a result of this high pressure. the powder becomes a mass ofcompacted material which i'orms a good conductor of heat and also a goodelectrical insulator.

The sheet metal of which the channel or sheath i is formed is an alloyof suitable metals adapted to withstand high temperatures for a longperiod of time. This alloy is well known in the art and the heatingelement comprising the sheath I, the compacted powder 4, I and theresistor I may be bent or curved to any desired shape 01' grid. Afterthe element is bent it will be necessary to use the underside I of thechannel as the top of the element, in which case the flange 2' willextend downwardly from the underside of the element. The flat top I"provides a maximum contacting surface, extending from side to side ofthe sheath, for engagement with the bottom of a cooking vessel.

In Figures 8 to 11, is shown a heater of the hot plate type comprisingtwo sheathed heatin elements i, l each of which was formed of apredetermined length of channel and subsequently bent or curved so thatit will cooperate with the other element to form a grid It. The ends ofthe elements are passed through openings in the top of a terminal box IIand secured therein in any suitable manner to form greaseproof Jointsbetween the edges of the openings and the ends of the elements. The boxIt is provided with upwardly extending'lugs I: which are pivoted at Iton any suitable stationary part II of a stove so that the heating gridmay be All swung upwardly relative to the cooking top it of the stove.

The convolutions of the grid are secured togather and the g d issupported as follows. a channel member ll extending across the undersideof the convolutions of the grid II is provided with spaced apartopenings II for receiving the portions of the flanges 2* overlying themember H. The depth of the flanges 2' is greater than the thickness ofthe material of which the channel member II is formed so that portionsof the flanges will extend through the openings Ii into the groove ofthe channel member. The protruding portions are burred or deformed tosecure the flanges in the openings. When the grid is spiral the channelmember I will extend diametrically across it and be arrangedsubstantially parallel to the axis of the pivotal connection for theterminal box Ii. A second channel member ll extends substantially atright angles to the member it across the underside of the portion of thegrid remote from the pivotal connection II. The member II is alsoprovided with spaced apart openings II for receiving the portions of theflanges 2' overlying the member II. The inner ends of the portions ofthe flanges received in the openings in the member II are also deformedto secure the flanges thereto. With this construction the convolutionsof the grid are firmly secured in spaced relationship to one another andyet they are free to expand and contract between the points ofconnection with the members i4, ii and the box H.

The channel members It and it rest on a re flector II which is removablycarried on a plurality of adjustable supports II which may be set screwsthreaded in lugs it formed on or secured to the underside of the cookingtop 20. The lugs project inwardly from the wall of the usual opening inthe cooking top to receive the hot plate and are so located relative tothe upper surface of the cooking top Ill that the top of the grid willbe positioned slightly above the upper sun face of the cooking top. Thereflector is pro-' vided with a rim II which extends upwardly around theouter convolutions oi the grid II to a point adjacent the underside of avessel resting on the grid. The rim and the bottom of the reflector arecut away at 12 to clear the ends of the sheathed elements which passdownwardly from the convolutions to the terminal box Ii located belowthe reflector.

By swinging the grid on its pivots Il to raise it clear ofthe-reflector, the latter may be readily removed from its supports itfor cleaning and polishing purposes. The terminals or lead-ins l areflexible, are insulated from one another and from the terminal box H inany suitable manner, and are directed through insulated openings 23therein to stationary contacts or direct to a switch (not shown).

The spiral grid type of hot plate enables a considerable length ofheating element or elements to be confined in a relatively small areasuch as would be covered by ordinary cooking vessels. To obtain the bestheating results it is not only necessary that the top surfaces i of theelements be flat to provide the maximum width of contact area (relativeto the width 01' each element) between the elements and a vesselsupported thereon but that the flat top surfaces I be flush so that themaximum contact area throughout 'the total length of the convolutionswill be obtained. Alter each element is curved or bent to the desiredshape, it is subjected to a high pressure to ensure that the tops I ofthe convolutlons are level. The rigidity of the continuous ribs orflanges 2 on the undersides of the elements tends to retain theconvolutions as set because the flanges resist any bending of theconvolutions in a vertical direction.

' The convolutions are firmly held irom shifting or twisting relative toone another by the channel members ll, l6 which are anchored firmly tothe flanges 2.

The stranded wire inlead 6 is preferably made of similar heat resistingalloy as the resistor 6 and is welded thereto as stated. This strandedwire 6 is oi greater cross-section than the wire of which the coil iswound so that it will cii'er very little resistance to the passage ofcurrent. This prevents the formation of objectionable heat in the leadsand at the ends of the sheath. This is important because it is advisableto use vitreous material at the ends of the sheath in order to make itnon-absorbent and proof against crumbling. The inlead 6 extends througha block 6'- of vitreous insulating material which is used to close theend of the sheath. This block is made to have intimate contact with theinner surface of the end of the sheath and also the inlead by means of afusion process.

As shown more particularly in Figs. 13 and 14 the rib or flange 2' canbe bent over or otherwise deformed where it projects into the groove ofthe channel member IE to secure the element to the channel member. Ifdesired, the attachment can be made in another manner still utilizingthe rib 2'. This modified form is shown in Figs. 15 and 16 and consistsin providing holes in the flanges 2* where they extend over the openingsII in the channel 16 and then inserting the pin I. through said holes tofasten the convolutions oi the element to the channel l8.

It is obvious that various modifications of my invention may be.madewithout departing from the spirit of the invention as defined by theaccompanying claims.

What I claim as new, and desire to secure by Letters Patent, is:

1. A sheathed electric heating element formed as a grid, the sheath ofthe element being formed of sheet metal having a flange dependingtherefrom: and a channel member having spaced apart openings forreceiving the portions of the flame overlying the member, the saidportions protrading into the groove of the channel member anddeformed tosecure them to the member.

2. An electric heating element having a sheet metal sheath provided witha flange, the element being formed .as a grid with the flange extendingdownwardly from the convlutions of the sheath; and a channel memberextending across, the underside of the grid and having spaced apartopenings in its upper wall to receive the portions or the flangeoverlying the said wall, the said flange being deeper than the thicknessof the said wall so that the portions in the openings will protrude intothe groove of the channel member and be deformed therein to secure thegrid to the member.

3. An electric heating element having a sheet metal sheath provided witha flange, the element being formed as a spiral grid with the flangeextending downwardly from the convolutions oi the sheath; and a channelmember extending acroas the underside of the grid and having spacedapart openings in its upper wall to receive the portions of the flangeoverlying the saidwall, a second channel member extending substantiallyat right angles to the first channel member across the underside of aportion of the grid, the second channel member also having openings inits upper wall to receive the portions of the flange overlying the lastmentioned wall, the said flange being deeper than the thickness of saidwalls so that the portions of the flange in the openings will protrudeinto the grooves of the channel members and be deformed therein tosecure the grid to the members.

4. An electric heater having a plurality of sheathed heating elementsformed as a grid, each element having two ends and each end having aterminal projecting therefrom for connection with an electrical supplycircuit; a terminal box having openings for receiving the ends of theelements, the said ends being secured in said openings, the sheath ofeach element being provided with a depending flange; and means forconnecting the flanges of adjacent convolutions together to hold partsof the convolutions in spaced relationship to one another, said meansincluding a channel member with slots in the web embracing portions ofthe flange.

5. An electric heater having a plurality of sheathed heating elementsformed as a grid, each element having two ends and each end having aterminal projecting therefrom for connection with an electrical supplycircuit; a terminal box having openings for receiving the ends of theelements, the said ends being secured in said openings, the sheath ofeach element being formed of sheet metal having a flange dependingtherefrom; a channel member extending across the underside of the gridand having spaced apart openings in its upper wall to receive theportions of the flanges overlying the said wall; a second channel memberextending substantially at right angles to the first mentioned channelmember across the underside of a portion of the grid remote from thebox, the second channel member also having openings in its upper wall toreceive the portions of the flanges overlying the last mentioned wall,the said flanges being deeper than the thiclmess of the said walls sothat the portions of the flanges in the openings will protrude into thegrooves of the channel member and be deformed therein to secure the gridto the members.

6. A heater constructed as set iorth in claim 4 in which the terminalbox is pivoted on a suitable stationary part; a reflector removablysupported on a stationary part beneath the grid and pro vided with a rimspaced from the outer periphery of the grid, the channel member beingsupported on said reflector, the reflector having an opening in itsperiphery to permit it to be readily removed from and replaced on itssupport.

Ill-MORE STANLEY SMITH.

